WEB Investigation of operational vibrations on the structural dynamics of glass fiber reinforced thermoplastic components
Due to their damping properties, short-fiber reinforced plastic (SFRP) components have become an essential part of modern powertrains with regard to Noise Vibration Harshness (NVH). The engine bracket is a suitable example. It transmits the engine-induced forces from the crankcase via the engine mount to the vehicle structure. For the investigation of the structural dynamics of plastic components under operational vibrations, multi-body simulations (MBS) are preferably used. Assuming reduced material models and non-deformable bodies, a sufficient prognosis of the structural dynamics of the entire powertrain can be made. However, this method is not suitable for the precise prediction of the structural dynamics of SFRP components. In the present work, a reduced simulation methodology is presented, which allows a prediction of the structural dynamics of plastic components with regard to operational vibrations under microscopic, material-specific modelling.
Operational vibration analyses allows an assessment of the overall structural dynamics of the entire powertrain. In order to characterize the operational vibration excitation in a reduced numerical model, the acceleration at the connection points of the plastic components to the powertrain has been investigated. A numerical acceleration input function has been derived and coupled to the FE-nodes of the joining points of the plastic components. Thus, an operational vibration excitation has been simulated and allows the prediction of the structural dynamics of the plastic components. The quality of the prediction of the structural dynamics of the SFRP components can be further improved, by using a material-specific, microscopic material model. Thereby, a sum function of transversal-isotropic stiffness and damping tensors with the corresponding probability distribution allows to generate a material database. Furthermore, the frequency-dependent, viscoelastic material behavior has been described using a Prony series formulation.
The presented simulation method has been applied to predict the structural dynamics of an engine bracket made of polyamide 6.6 with 50 weight percent glass fibers. Compared to the approach of a MBS, the presented methodology allows a more accurate prediction of the structural dynamics of the engine bracket. Further investigations focus on the precise calibration of the numerical acceleration input function to characterize the operational vibrations.